The present invention generally relates to vertical magnetic recording medium, magnetic storage apparatus and manufacturing method of a vertical magnetic recording medium, and more particularly to a vertical magnetic recording medium having a layer confining a magnetic flux between a substrate and a recording layer.
In recent years, the magnetic storage apparatuses used for personal computers or home movie recording apparatuses generally have a large storage capacity of 100 GB or more in relation to the need of recording motion pictures. Further, it is predicted that the demand of larger storage capacity and reduced cost of the magnetic disk apparatuses becomes more stringent in the future.
In the in-plane magnetic recording technology used in the currently marketed magnetic disk apparatuses, it is recognized that the surface recording density of 200 Gbit/inch2 is the maximum recording density achievable with this conventional technology.
As the magnetic recording technology that can break through this technological limit, the technology of vertical magnetic recording draws attention again, in view of the nature of the vertical magnetic recording technology that can reduce the effect of the demagnitization field formed by the magnetization of the magnetic recording layer. With the vertical magnetic recording technology, it is predicted that the recording density of 1 Tbit/inch2 or more is achieved.
With the vertical magnetic recording technology, however, problems noted below are pointed out.
First, with decrease of the track width, there occurs a decrease of core width in the magnetic pole of the magnetic head, and the recoding magnetic field formed with the magnetic head is reduced.
Second, there is a tendency that the magnetic flux spreads laterally in the magnetic recording medium located downward of the magnetic pole of the magnetic head at the time of the magnetic recording, and there arises a problem of so-called side erasing or side writing, in which the information in the adjacent track is erased.
Third, there occurs increase of medium noise of the recording layer with increase of linear recording density, wherein this increase of the medium noise is attributed mostly to the noise formed in the magnetization transition region (transition noise).
Fourth, it is difficult to control the core width and position of the magnetic pole in the recording head and the reproducing head.
Particularly, the foregoing second problem appears conspicuous in the so-called two-layer vertical magnetic recording medium having a soft magnetic backing layer between the substrate and the recording layer. It should be noted that this two-layer vertical magnetic recording medium is thought as a promising recording medium capable of realizing a high density recording.
More specifically, there occurs a decrease of recording magnetic field in such a two-layer vertical magnetic recording medium as a result of the spreading of the magnetic flux as the magnetic flux exiting from the end point of the miniaturized single pole magnetic head extends toward the soft magnetic backing layer covering the entire magnetic disk surface, and there occurs an increase of side erasing phenomenon or increase of length of the magnetic transition region in the recording layer along the track direction.
In view of the foregoing, there is a proposal of providing a region underneath the track formed magnetically in the recording layer so as to guide the magnetic flux toward the soft magnetic backing layer and suppress the spreading of the magnetic flux at the time of the recording (reference should be made to Patent References 1 and 2).
FIG. 1 shows such a vertical magnetic recording medium 100 described in the foregoing Patent Reference 2.
Referring to FIG. 1, the vertical magnetic recording medium 100 includes a soft magnetic backing layer 102 between a substrate 101 and a recording layer 103, wherein there is provided a soft magnetic part 102a in the soft magnetic backing layer 102 along a track region 103a, along which magnetic recording of information is made into the recording layer 103, such that the magnetic flux is guided preferentially to the soft magnetic backing layer 102 along such a soft magnetic part 102a. Further, there is formed a non-magnetic part 102c along an inter-track region 103b formed between a pair of adjacent track regions 103a such that penetration of the magnetic flux into such a inter-track region 103b is reduced. Thereby, the magnetic flux from the magnetic pole of the magnetic head is concentrated to the soft magnetic part 102a of the soft magnetic backing layer 102 after passing through the recording layer 103, and thus, the problem of lateral spreading of the magnetic flux and associated side-erasing of the information are suppressed.
Patent Reference 1 Japanese Laid Open Patent Application 2003-16621 official gazette
Patent Reference 2 Japanese Laid Open Patent Application 2003-16622 official gazette